1. Field of the Invention
The invention relates to an automatic sheet-feeding scanner, and more particularly to an automatic sheet-feeding scanner having a feeding mechanism for transporting a document horizontally past a scan region of the scanner.
2. Related Art
For an automatic sheet feeder used in a conventional document scanner, rollers for transporting an original to and from the scan region are disposed on two sides of a scan region at a height higher than that of a scan platen in the scanner. The original is firstly transported by the rollers disposed on the upstream side of the scan region and then by the rollers disposed on the downstream side of the scan region.
FIG. 3 is a schematic illustration showing a conventional document scanner. Referring to FIG. 3, the document scanner includes an automatic sheet feeder 300 and a flatbed scanner 400. The flatbed scanner 400 includes a housing 410, a transparent platen 420, a scanning module 430 and a guide rod 440. The scanning module 430 may slide along the guide rod 440 to acquire an image of a stationary document placed on the transparent platen 420. In addition, the scanning module 430 may also acquire an image of the document D transported past a scan region 350.
The automatic sheet feeder 300 has a document supply tray 310, a document discharge tray 320 and a sheet-feeding mechanism 330. The sheet-feeding mechanism 330 includes a feeding roller 331 and three pairs of transporting rollers 332, 333 and 334. The feeding roller 331 feeds the sheets from the document supply tray 310 into a path 340 one by one. Then, the transporting rollers 332 transport the document D to and past the scan region 350. Next, the feeding rollers 333 and 334 transport the document D out of the paper path 340 to reach the document discharge tray 320. At the moment that the trailing edge of the document D leaves the feeding rollers 332 and drops off, a shock is applied to the document D, changing the distance between the document D and the scanning module 430 and affecting the quality of the scan image of the document D. Particularly when the photo image sensor used in the scanning module 430 is a contact-type image sensor (CIS), the influence of the shock to the scan image becomes evident because the CIS has a shorter depth of field. In such circumstance, the scan image is often blurred or defocused.
Thus, it is an important object of the invention to provide an automatic sheet-feeding scanner effectively eliminating the instantaneous shock to the scan image at the moment the original leaves the rollers.